Electron gun and mounting therefor



1 April 1952 v. c. CAMPBELL ELECTRON GUN AND MOUNTING THEREFOR FiledJuly 19, 1950 Fig.1.

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Patented Apr. 8, 1952 2,592,242 ELECTRON GUN AND MOUNTING THEREFOR VonC. Campbell, Syracune, N. Y., minor to General Electric Company, acorporation of New York Application July 19, 1950, Serial No. 174,769

v 4 Claims.

The present invention relates to an improved electron gun structure andmounting therefor and more particularly to a simplified gun structure ofthe ion trap type.

Cathode ray tubes employing an ion trap for separating unwanted ionsfrom the electron stream have been widely used commercially. In one formof tubes of this type the electron gun is designed to impart to both theions and elec-' trons a transverse deflection by subjecting them to atransverse component of electrostatic field. The electrons only arereturned to the axis of the cathode ray tube by means of anelectromagnetic field and the ions suitably collected on a surface lyingoff the axis of the tube.

It is an important object of the present invention to provide animproved and simplified gun structure for use in an ion trap type oftube and including a simplified mounting therefor.

My invention will be better understood by reference to the followingdescription taken in connection with the accompanying drawing and itsscope will be pointed out in the appended claims. In the drawing Fig. 1is an elevational view partially in section of a cathode ray tubeembodying my invention. Fig. 2 is an enlarged sectional view of the neckof the tube of Fig. 1 showing the details of construction of theelectron gun and Fig. 3 illustrates a modified gun structure embodyingmy invention.

Referring now to the drawing I have shown my invention embodied in acathode ray tube of the metal envelope type including a generallyconical metal part I having a glass face plate 2 sealed A glass neck -3including a flare or funnel 4 is sealed to the smaller end of the metalcone I. The neck is closed at the lower end thereof by a stem 5 ofconventional construction through which the various lead-in conductorsare sealed and which is provided with an exhaust tubulation I throughwhich the device is evacuated.

The inner surface of the face plate 2 is provided with a fluorescentcoating 8 and the neck 3 is provided with a conducting inner surface 9which extends from the metal cone to the upper end of the gun structuredesignated generally by the numeral II]. The coating may be applied inany suitable manner and in accordance with a method well known in theart, a graphite suspension is painted on the interior surface of theneck.

The gun structure I0 in accordance with my invention includes agenerally cylindrical grid cylinder II. The end of the cylinder lltoward the screen is cut at an angle with respect to the axis of thetube and is effective in cooperation with the conducting surface 9, whena direct current voltage difference is applied therebetween to impart atransverse deflection to electrons and ions emanating from the gun. Thecylinder II supports a transverse metal disc I2 having a central gridaperture I3 and a cylindrical cathode I4 having a closed end locateddirectly behind the rid aperture and coated with a suitable electronemissive coating designated by the numeral I5. The cathode cylinder I 4is suitably supported from the grid cylinder II by an insulating disc I6which is spaced from the disc I 2 by a collar II. The cathode assemblyalso includes a suitable filamentary heater member I8 received withinthe cathode cylinder. The gun assembly thus far described is supportedfrom the stem by means of a. plurality of lead-in conductors of whichtwo are visible in Fig. 2, and designated by numerals I9 and 20. Theconductors are directed outwardly at their upper ends and bonded to acollar 2| which is welded to the lower end of the grid cylinder II. Thegrid cylinder I I is further supported and positioned within the neck 3of the cathode ray tube by a pair of spaced insulating discs such asmica discs 22 and 23. The lower disc 22 bears against the flange ofcollar 2| and the upper disc 23 is supported by a plurality of hollowrivets 24 carried by conductors 25 and 26. These latter conductors aresealed into the stem 5 but preferably do not extend to the exterior sidethereof.

A metal ring 21 having a plurality of pellets of getter material 21'positioned on either surface thereof and preferably on the outer surfacethereof is positioned between the insulating discs 22 and 23 andsecured, as illustrated, to the conductors 25 and 2B. This constructionlargely confines the getter material to a localized area of the envelopewall. As is well understood, the getter may be flashed by suitableapplication of high frequency energy to the tube during processing ofthe tube.

The connections with the heater element III are made with two suitablelead-in conductors 28 and 29, the cathode cylinder is connected with alead-in conductor 30, and the grid cylinder as previously indicated isconnected with conductors I9 and 20. All of the lead-in conductors whichare needed for energizing the various elements are connected to suitableterminal prongs 3| secured to a conventional insulating tube base 32which is bonded to the base of the tube by basing cement 33.

As is well understood by those skilled in the art, in the operation ofthe device described above, electrons are emitted from the cathodesurface I5. when it attains a suitable operating temperature. Theseelectrons move in the form of a beam toward the screen 8 of the tubeunder the control of the grid including the transverse disc I2, and theanode potential which is impressed on the cone I and the conductivecoating 9. The control or signal voltage is impressed on the gridcylinder I I to vary the intensity of the beam in accordance with thereceived signal. With the bias cut 01' the grid cylinder II, the beam isgivena deflection in a transverse direction and this deflection issubstantially equal for both electrons and any ions that may be present3 in the beam. The electrons only are returned to the axis of the tubeby the action of a magnetic field transverse to the axis of the tube andproduced by a suitably magnetized ring 34 supported on the outside ofthe tube on a resilient sleeve 36. A smaller and weaker permanent magnetmember 35 located in spaced relationship to the ring 34 provides asuitable means for just bringing the electron beam back to the center ofthe screen. It may be moved longitudinally of the tube and also rotatedwith respect to the tube to produce the final adjustment. Thearrangement of magnets described is more fully described and claimed inWainwright Patent 2,456,474 dated December 14, 1948. It will be wellunderstood that the beam is focused and deflected to scan the screen bymeans of suitable magnetic means which are associated with the exteriorof the tube in use and which are not shown in the drawing.

It has been found that in spite of the voltage variations on the gridcylinder l l due to the grid signal, it cooperates effectively with theconductive coating of the wall 9 to provide the necessary transversecomponent of electrostatic field to deflect both the ions and electronstoward the wall of the tube so that the magnetic field returns only theelectrons to the axis of the tube leaving the ions to be collected bythe conducting surface 9. In a preferred embodiment of my invention theangle of the bias cut grid cylinder is approximately 16 as illustratedin the drawing.

In some cases it may be desirable to collect the ions on a metal surfaceand in that case a tubular metal member may be supported from the gunstructure and electrically connected with the conductive coating 9 andin this way form effectively an extension of that coating. Such amodification is shown in Fig. 3 in which the gun structure is the sameas that shown and described in Figs. land 2. The additional' cylinder isillustrated at 31 and is supported from the gun structure by means ofsuitable glass stalks 38 which are sealed to suitable lugs 39 welded tothe cylinder ll of the grid and to the cylinder 31. A suitable disc ismounted on the upper end of the cylinder 31 and provided with abeam-limiting aperture 40. Suitable spring contact fingers ll carried bythis disc and engage the conductive surface of the inner wall of theenvelope. Electrically, the operation of the modification described inconnection with Fig. 3 is identical with that described in connectionwith Figs. 1 and 2.

While I have described particular embodiments of my invention, it willbe apparent to those skilled in the art that changes and modificationsmay be made without departing from my invention in its broader aspects,and I intend, therefore, in the appended claims to cover all suchchanges and modifications as fall within the true spirit and scope of myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A cathode ray tube comprising an envelope including a cylindricalneck, an electron gun supported within said neck comprising a generallycylindrical control grid member, a cathode supported from and withinsaid grid member, said grid member terminating in a plane making anacute angle with the axis thereof at one end and provided with anoutwardly extending flange at the other end thereof, a pair of spacedinsulating disks interposed between said cylindrical control grid memberand the neck of said envelope, one of said insulating disks engagingsaid flange and a getter ring surrounding said grid member and supportedin the space between said insulating disks.

2. A cathode ray tube comprising an envelope including a cylindricalneck, an electronic gun supported within said neck comprising agenerally cylindrical control grid member, a cathode supported from andwithin said grid member, said grid member being provided at one end withan outwardly extending flange, a pair of spaced insulating disksinterposed between said electrical control grid member and the neck ofsaid envelope, one of said insulating disks engaging said flange and agetter ring surrounding said grid member and supported in the spacebetween said insulating supports.

3. A cathode ray tube comprising an envelope including a fluorescentscreen at one end, an elongated cylindrical neck at the other end, aconductive surface within said envelope extending down the inner wall ofsaid neck portion, an electron gun supported within said neck andincluding a control grid cylinder, a cathode supported within said gridcylinder, an apertured transverse wall supported from and conductivelyconnected to said control grid cylinder on the side of said cathodenearer said screen, said grid cylinder having the end toward said screenterminating in a plane extending at an acute angle with respect to theaxis of said grid cylinder and operable in response to a voltagedifference between said grid and said conductive surface to subjectelectrons emanating from said gun to a component of electrostatic fieldtransverse with respect to the axis of said grid cylinder.

4. A cathode ray tube comprising an envelope having a tubular portion, aconductive surface on the inner wall of said tubular portion, anelectron gun supported within said tubular portion and including acontrol grid cylinder, a cathode supported within said cylinder, anapertured transverse wall supported from and conductively connected tosaid control grid cylinder intermediate the ends thereof, said gridcylinder having the end away from said cathode terminating in a planeextending at an acute angle with respect to the axis of said gridcylinder and cooperating with the conductive surface on said tubularportion to subject electrons emanating from said gun to a component ofelectrostatic field transverse with respect to the axis of said gridcylinder in response to a voltage difference between said grid cylinderand said conductive coating.

VON C. CAMPBELL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,185,378 Maloif et a1. Jan. 2,1940 2,225,901 Bruche Dec. 24, 1940 2,264,274 Broadway Dec. 2, 19412,268,194 Glass Dec. 30, 1941 2,295,038 Hergnrother Sept. 8, 19422,297,429 Paehr Sept. 29, 1942 2,443,916 Kelar June 22, 1948 2,456,474Wainwright Dec. 14, 1948 2,496,127 Kelar Jan. 31, 1950 2,515,305 KelarJuly 18, 1950

